[show abstract][hide abstract] ABSTRACT: Recently, we found strong overexpression of the mucin-type glycoprotein podoplanin (PDPN) in human astrocytic brain tumors, specifically in primary glioblastoma multiforme (GB). In the current study, we show an inverse correlation between PDPN expression and PTEN levels in primary human GB and glioma cell lines, and we report elevated PDPN protein levels in the subventricular zone of brain tissue sections of PTEN-deficient mice. In human glioma cells lacking functional PTEN, reintroduction of wild-type PTEN, inhibition of the PTEN downstream target protein kinase B/AKT, or interference with transcription factor AP-1 function resulted in efficient downregulation of PDPN expression. In addition, we observed hypoxia-dependent PDPN transcriptional control and demonstrated that PDPN expression is subject to negative transcriptional regulation by promoter methylation in human GB and in glioma cell lines. Treatment of PTEN-negative glioma cells with demethylating agents induced expression of PDPN. Together, our findings show that increased PDPN expression in human GB is caused by loss of PTEN function and activation of the PI3K-AKT-AP-1 signaling pathway, accompanied by epigenetic regulation of PDPN promoter activity. Silencing of PDPN expression leads to reduced proliferation and migration of glioma cells, suggesting a functional role of PDPN in glioma progression and malignancy. Thus, specific targeting of PDPN expression and/or function could be a promising strategy for the treatment of patients with primary GB.
[show abstract][hide abstract] ABSTRACT: Deletions of chromosomal arms 1p and 19q are frequent in oligodendroglial tumours and linked to radio- and chemotherapy response as well as longer survival. The molecular mechanisms underlying this clinically important association are as yet unknown. Here, we studied the peroxiredoxin 1 (PRDX1) gene at 1p34.1 for promoter methylation and expression in primary gliomas and investigated its role in radio- and chemosensitivity of glioma cells in vitro. In total, we screened primary glioma tissues from 93 patients for methylation of the 5'-CpG island of PRDX1 by sodium bisulfite sequencing. PRDX1 mRNA and protein expression levels were determined in subsets of the tumours by quantitative PCR and western blot analysis, respectively. PRDX1 hypermethylation and reduced expression were frequently detected in oligodendroglial tumours and secondary glioblastomas, but not in primary glioblastomas. In oligodendroglial tumours, both PRDX1 hypermethylation and reduced mRNA expression were significantly associated with 1p/19q-deletion. Stable knockdown of PRDX1 by lentiviral transduction of short-hairpin (sh)RNA constructs significantly increased apoptosis and reduced cell viability of Hs683 glioma cells exposed to ionizing irradiation or temozolomide in vitro. Taken together, our findings indicate that epigenetic silencing of PRDX1 is frequent in 1p/19q-deleted oligodendroglial tumours and likely contributes to radio- and chemosensitivity of these tumours.